In the manufacture of non-woven products including reactive materials (such as activated carbon), whether for the manufacture of filters, clothing, or other non-woven products, it is highly desirable to utilize the active material in some sort of particulate form because in that form most active materials have their maximum activity. During the conventional production of non-woven webs using particulate active material by the conventional wet laid process (the wet laid process being describe per se in U.S. Pat. No. 4,349,414) if the active material is in particulate form it loses a significant portion of its reactivity because the liquid dissolves part of the active material and is drawn away from the web during the production process, and for other reasons depending upon the particular materials involved. An air laid (see U.S. Pat. No. 5,779,847 for example) product has been developed which avoids the degradation of the reactivity of the particulate material to a significant extent during the manufacture of non-woven webs, however the air laid process is significantly slower than the wet laid process, and therefore there is much lower productivity and higher costs for the products produced.
According to the present invention a method and product are provided which utilize either the wet laid process, or preferably the foam process (as described, for example, in U.S. Pat. No. 5,904,909 and in co-pending application Ser. No. 09/260,024 filed Mar. 2, 1999, the disclosures of which are hereby incorporated by reference herein). According to the present invention it is possible to obtain the speed and productivity of the wet laid or foam processes in the manufacture of non-woven webs of fibrous material containing an active at least partly particulate material (typically at least about 80% particulate form), while maintaining substantially optimum reactivity of the active particulate material. This is accomplished according to the present invention by providing a liquid, or preferably foam, slurry including the active particulate material between first and second webs primarily of fibrous material during the manufacture thereof by the wet laid, or preferably foam, process, and substantially at or after the combination thereof withdrawing liquid, or foam and liquid, from the composite and then drying the composite to produce a final non-woven web with active material therein having substantially optimum reactivity. Maintenance of substantially optimum reactivity can also be achieved by making the slurry using a particulate material no more than about ten seconds prior to the initiation of the withdrawal of the liquid and/or foam from the composite web, and by using substantially pure water (which includes distilled, deionized, and reverse osmosis water) as the liquid for the wet laid process, or for use in the production of the foam for the foam process or slurry.
By practicing the invention the speed of production and productivity may be high. The invention can be accomplished utilizing already known equipment, such as shown in co-pending application Ser. No. 09/260,024 for the foam process, or for the wet laid process U.S. Pat. No. 4,349,414.
The invention can be practiced with a wide variety of active materials, such as disclosed in U.S. Pat. No. 5,779,847, and with a wide variety of fibers including cellulose fibers, glass, aramid, synthetic (such as polyester, polypropylene, polyamide), etc. The active material is preferably at least about 80% particulate material, but some fibrous material can also be utilized. For example carbon fibers can be combined with powdered activated carbon as an active component utilized in the practice of the invention.
According to one aspect of the present invention there is provided a method of making a non-woven web of fibrous material containing an active at least partly particulate material, comprising: a) Making first and second webs primarily of fibrous material using the wet laid or foam processes. b) Forming a liquid or foam slurry including active at least partly particulate material. c) Providing the slurry from b) between the first and second webs during manufacture thereof, so as to provide a composite web. And, d) substantially at or after c), withdrawing liquid, or foam and liquid, from the composite web, and then drying the composite web so as to produce a final non-woven web with active material therein having substantially optimum reactivity.
In the invention, preferably a) and b) are practiced using substantially pure water as or in the liquid or foam for slurrying the active material and for use in the wet laid or foam process. In the invention one of the preferred materials in the practice of b) is the utilization of activated carbon as at least part of the particulate active material (or substantially all thereof), and d) may also be practiced using titanium dioxide as a particulate material in the liquid or foam slurry. Preferably a) is practiced using the foam process, and b) is practiced using the foam slurry. Typically b) is practiced by mixing at least the particulate part of the active material with the foam slurry no more than about ten seconds before the practice of d). Typically a) through d) are practiced at a carbon loading of between about 0.25-1 g/cm3, and to produce a product having an air permeability over 3000 liters per square meter per second at 200 Pa.
The invention may further comprise making the final non-woven web into a useful product, such as a filter (including pleated filters) for automotive, household, or industrial use, making clothing, or making other types of materials.
The method may also further comprise e) providing at least one other liquid or foam web or slurry, and f) combining the at least one other liquid or foam web or slurry with other webs and slurry substantially at or prior to d) so that the final non-woven web produced includes the at least one other liquid or foam web. For example in the method b) and e) are practiced by mixing at least the particulate part of the active material and titanium dioxide with the foam slurry no more than about ten seconds before the practice of d). Also a), b), and e) may be practiced using substantially pure water in the foam for slurrying the active material and for use in the foam process.
The invention also relates to a non-woven web with active material therein having substantially optimum reactivity, made by any of the processes as described above. Especially when the foam process is utilized according to the invention, there are an almost infinite variety of sizes and types of fibers and active materials that may be utilized, and provided in the final web.
According to another aspect of the invention there may be provided a method of making a non-woven web of fibrous material containing an active material, comprising: a) Making first and second webs primarily of fibrous material using the wet laid or foam processes. b) Forming a liquid or foam slurry including active material. c) Providing the slurry from b) between the first and second webs during manufacture thereof, so as to provide a composite web. And d) substantially at or after c), withdrawing liquid, or foam and liquid, from the composite web, and then drying the composite web so as to produce a final non-woven web with active material therein having substantially optimum reactivity. In the method b) may be practiced using at least one of active material fibers, e.g. carbon fibers, and active material particles, e.g. carbon particles as described above.
It is the primary object of the present invention to provide a simple, high productivity, and effective method of making a non-woven web of fibrous material with active material therein having substantially optimum reactivity, and the web so produced. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.